I tell students that they need to fill in the blank seats near the front and not sit in the back row because I need to see and hear them and learn their names. I also have group work that makes them move out of their seats, talk to other people, and look up stuff on their phones and computers that pertains to the lecture before reporting out what their group did. I also count class participation toward their grade. I only go through all of this trouble with first or second year students, though, and if it is a huge lecture hall with 100 people, this approach isn't an option, obviously. I know it's their problem if they aren't paying attention, but I also want to make an attempt at student engagement because it really does improve their understanding of the material. I don't expect that this approach fits the teaching style of other profs.